1. Field of the Invention
The present invention relates to a system and method for controlling layer 3 (L3) handover of a mobile node.
2. Description of the Related Art
At present, the Internet is based on Internet protocol version 4 (IPv4). In IPv4, a source incorporates a source address and a destination address into a packet in order to transmit the packet to a destination via the Internet. An IP address used in IPv4 consists of 32 bits, which allows about 4 billion hosts to connect to the Internet. However, due to special address use, subnetting, network address allocation, and the like, the number of hosts that can actually connect to the Internet is more limited. Furthermore, with the spread of the Internet and increase in multimedia traffic, mobile communication terminals, customer information appliances, and the like, as well as computers, have been adapted to connect to the Internet. There are a great number of customer information appliances, including mobile communication terminals, televisions, and refrigerators, that cannot all connect to the Internet due to insufficient availability of IPv4 addresses. To overcome the problem of insufficient available IP addresses and to achieve high-performance Internet by making IPv4 more efficient, IPv6 technology has been developed.
Internet protocol version 6 (IPv6) is based on a 128-bit address system and provides fluent IP addresses in comparison with the 32-bit IPv4. Since the 128-bit address system increases the amount of content in a routing table that a router uses to determine a route, time taken to search for a suitable route can increase. Fortunately, the time taken to search for a route in a routing table can be shortened by having more layers in the IPv6 address system than in the IPv4 address system.
With the advanced IPv6, high-performance Internet capable of coping with rapidly increasing Internet traffic and spread of multimedia traffic can be provided. Meanwhile, IP addresses allocated to hosts consist of a network identifier and a host identifier. The network identifier is unique information for identifying a network to which hosts are connected, and the host identifier is unique information for identifying a host in the network. The host allocated the IP address generates a socket address using the IP address and a port number of a transfer layer and establishes a connection with other hosts using the socket address.
Once one host (a first host) is connected to another host (a second host), an IP address of the first host should be kept unchanged while the connection is maintained. When the first host connected to the second host moves to another network in a mobile environment, the network identifier must be changed. This changes the IP address allocated to the first host. Since the IP address change leads to change in a socket address, the existing connection is released. Accordingly, re-connection must be attempted.
To solve the problem of the connection release caused by a host's movement to another network, the Internet Engineering Task Force (IETF) proposes mobile IPv6 (hereinafter, referred to as “MIPv6”) protocol. MIPv6 protocol allows an existing connection to be maintained even though a mobile node (MN) moves to another network. In other words, MIPv6 protocol provides a mechanism for enabling a connection with another host (“correspondent node (CN)”) on the Internet to be kept unchanged even though a mobile node on the Internet connected to the correspondent node moves to another place.
Meanwhile, developments in communication technology include the building of wireless networks such as a cellular network, a wireless LAN, a Wibro network, and the like. The wireless network allows users to use various multimedia services, such as voice over Internet protocol (VoIP), video phone, IP-TV, and video on demand (VoD), in a wireless environment. However, if a serving base station is changed due to a user's movement in the wireless environment, service can be blocked. Accordingly, handover technology is required to provide seamless service even when users move. A handover can be classified into a layer 2 (L2) handover and a layer 3 (L3) handover. The L2 handover occurs when a user moves to another base station, and the L3 handover occurs when a user moves to another IP subnet. The L2 handover is performed by a cellular network, a wireless LAN, and a Wibro network, and the L3 handover is performed through the above mobile IP (MIP), which is for using the same IP address allocated to a user.
A MIPv6 network includes a home agent (HA), an MIPv6 mobile node, a number of routers, base stations, and a correspondent node (CN). The mobile node is a sort of terminal for enabling a user to receive Internet service, and the routers relay a packet to the mobile node. The home agent manages an address of the mobile node, and the correspondent node is an arbitrary host on the Internet that provides multimedia service to the mobile node. A handover occurs when the mobile node moves to another base station.
In describing a handover process in an MIPv6 network, it is assumed that the mobile node moves from the second base station belonging to the home agent to the third base station belonging to the second router. First, the mobile node in a coverage area of the first router serving as the home agent transmits and receives data to and from the correspondent node. If a user of the mobile node moves from the coverage area of the first router to a coverage area of the second router, the mobile node senses the movement to the second base station. Here, the mobile node, when moving into the coverage area of the second router, senses the movement in an L3 state through old access reachability check.
After recognizing the necessity of L3 handover, the mobile node transmits a router solicitation (RS) message to the second router. Upon receipt of the RS message, the second router generates a router advertisement (RA) message including its own prefix information and the like and transmits it to the mobile node. In response to the router advertisement message, the mobile node extracts the prefix information and generates a care-of-address by itself (CoA).
The mobile node transmits a binding update (BU) message to the home agent to report the care-of-address generated previously. The home agent registers the care-of-address contained in the binding update message with its own database and responds by transmitting a binding update acknowledgment message to the mobile node.
After the binding update procedure is performed, the correspondent node still transmits data to the mobile node via the home agent. The home agent encapsulates the data from the correspondent node into a new care-of-address of the mobile node and tunnels it to the mobile node.
Meanwhile, the mobile node can transmit data to the correspondent node via the second router. However, the mobile node performs a binding update process with the correspondent node for router optimization to remove the tunneling process. This binding update process is performed through the exchange of the binding update message and the binding update acknowledgement message. After the binding update, the mobile node communicates data with the correspondent node directly, not via the home agent.
The L3 handover process includes a movement sensing process, a care-of-address generation process, and a binding update process. The movement sensing process takes 300 ms, and the care-of-address generation process takes about 1 second. Finally, the binding update process takes 10 ms.
In MIPv6, the L3 handover occurs after the L2 handover as described above, and the L3 handover can take 1.3 seconds or more. Thus, it is necessary to reduce the care-of-address generation time, which is about 1 second and accounts for most of the time taken to perform a handover.